Position measuring device

ABSTRACT

A position measuring device for detecting the spatial position of a movable element in relation to a base body, the device including a linear measuring device that measures a distance between a movable element and a base body and an angle-measuring apparatus that measures an angle between the movable element and the base body. A light source that directs light along a beam path, a detector within the beam path and a grating within the beam path between the light source and the detector. For measuring the angle, the beam path extends between the movable element and the base body so that an intensity strip pattern is created by illuminating the grating by the light source, whose position relative to the detector is a measure of the angle.

Applicants claim, under 35 U.S.C. 120 and 365, the benefit of priorityof the filing date of Oct. 16, 2002 of a Patent Cooperation Treatypatent application, copy attached, Serial Number PCT/EP02/11544, filedon the aforementioned date, the entire contents of which areincorporated herein by reference, wherein Patent Cooperation Treatypatent application Serial Number PCT/EP02/11544 was not published underPCT Article 21(2) in English.

Applicants claim, under 35 U.S.C. 119, the benefit of priority of thefiling date of Oct. 23, 2001 of a German patent application, copyattached, Serial Number 101 51 563.4, filed on the aforementioned date,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a position measuring device fordetecting the position of a movable element in relation to a base body.

2. Description of the Related Art

Position measuring devices are known from both DE 195 34 535 C2 and DE35 04464 C1, by which the spatial position of a movable element inrelation to a base body is determined by several telescoping rods, whichare spatially arranged with respect to each other, through linearmeasurements in the telescoping rods. In DE 35 04 464 C1 the purpose ofsuch a position measuring device is said to be the checking of thepositioning accuracy of a program-controlled device arm.

The disadvantage of these position measuring devices lies in thearrangement of several telescoping rods for determining the position ofthe movable element in three degrees of freedom. The telescoping rodsmust be arranged in a predetermined manner with respect to each other inorder to determine the spatial position of the movable element by apredetermined calculation rule from the connection between the lengthsof the telescoping rods.

SUMMARY AND OBJECTS OF THE INVENTION

It is therefore an object of the present invention to simplify thestructure of a position measuring device for detecting the position of amovable element in relation to a base body.

This object is attained by a position measuring device for detecting thespatial position of a movable element in relation to a base body, thedevice including a linear measuring device that measures a distancebetween a movable element and a base body and an angle-measuringapparatus that measures an angle between the movable element and thebase body. A light source that directs light along a beam path, adetector within the beam path and a grating within the beam path betweenthe light source and the detector. For measuring the angle, the beampath extends between the movable element and the base body so that anintensity strip pattern is created by illuminating the grating by thelight source, whose position relative to the detector is a measure ofthe angle.

An advantage of the present invention is perceived to lie in that themovement of the movable element in at least three degrees of freedom,namely a translational and two rotational ones, can be measured by asingle telescoping leg of simple construction.

Details and further advantages ensue from the following description ofexemplary embodiments by the drawings.

Shown are in:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of a position measuring device for measuringthe spatial position of a moved element in accordance with the presentinvention;

FIG. 2 shows a functional principle of the angle-measuring apparatus ofthe position measuring device in FIG. 1;

FIG. 3 shows a further embodiment of a position measuring device formeasuring the spatial position of a moved element by interferometriclinear measurements in accordance with the present invention;

FIG. 4 illustrates a possible use of the position measuring devices ofFIGS. 1-3 for detecting a moved element in six degrees of freedom; and

FIG. 5 illustrates a possible use of the position measuring devices ofFIGS. 1-3 in a machine.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S) OF THE INVENTION

The basic structure of a position measuring device 10 in accordance withthe present invention is schematically represented in FIG. 1. Itincludes a base body 1 with a joint 2, by which a support 3 is seated,pivotable in all directions, on the base body 1. The support 3 isembodied telescopingly and includes least two tubes 3.1 and 3.2, whichcan be pushed into each other. The one tube 3.1 is seated as a telescopeelement on the joint 2, and the other tube 3.2 is seated, pivotable inall directions, by a further joint 4 on the element 5 to be measured.

The movement of the element 5 in the longitudinal direction of thesupport 3 is measured by a linear measuring device 6. The latterincludes a scale 6.1 fastened on one of the tubes 3.1, and of a scanningelement 6.2 fastened on the other tube 3.2. Several such linearmeasuring devices can be employed for redundant measuring and these arein particular arranged symmetrically with respect to a centeredconnecting line located between the two joints 2, 4, such as representedin FIG. 5 of DE 197 03 735 C2.

The lateral displacement of the element 5 in relation to the base body 1results in a pivot movement of the support 3 with respect to the basebody 1. This pivot movement is measured by an angle-measuring apparatus7. The latter includes a light source 7.1, a detector 7.2 and a grating7.3. The light source 7.1 is fixedly arranged in the center of rotationD4 of the joint 4 on the element 5 and transmits a divergent light beamL along the support 3 (FIG. 2). The detector 7.2 is located inside thelight beam L in the center of rotation D2 of the joint 2 on the basebody. The grating 7.3 is located at a fixed distance in front of thedetector 7.2 and is also fastened on the base body 1 and in this way isfixedly assigned to the detector 7.2. By illuminating the grating 7.3 bythe divergent light beam L, an intensity strip pattern M is generated,whose position in relation to the detector 7.2 is a measure of the pivotmovement of the support 3, and therefore of the lateral displacement ofthe element 5.

Because of the arrangement of the light source 7.1 and the detector 7.2directly on the base body 1, or the element 5 to be measured, errors inthe joints 2 and 4, as well as translational errors of the support 3 donot enter into the angular measurement. The beam path for angularmeasurement extends between the movable element 5 and the base body 1.Here, the light source 7.1 is arranged in one of the centers of rotationD2, D4, and the center of the light-sensitive elements of the detector7.2 in the other one of the centers of rotation D4, D2. It is possiblein a manner not represented to arrange the light source 7.1, as well asthe detector 7.2, in one center of rotation D2, D4, and aretro-reflecting element in the other center of rotation D4, D2. Beamsplitting is advantageous in connection with this, so that the lightbeam passes through the grating 7.3 in only one direction. In that casethe detector 7.2 or the light source 7.1 is located at the site of thecenter of rotation D2 or D4 which is mirrored or depicted by the beamsplitter. The grating 7.3 is spatially fixedly assigned either to thelight source 7.1 or the detector 7.2.

For measuring the lateral displacement of the element 5 in alldirections transversely to the longitudinal direction of the support 3,i.e. the pivot angle of the element 5 around the center of rotation D2,the grating 7.3 is a two-dimensional structure, for example atwo-dimensional cross grating, so that a two-dimensional intensitypattern M is created during illumination, whose position relative to thedetector 7.2 is a measure for the angle of the element 5 with respect tothe base body 1.

The detector 7.2 preferably includes several light-sensitive elementsfor generating several electrical sinusoidal scanning signals which arephase-shifted in relation to each other. In the illustrated example, theplanar center of the light-sensitive elements for generating a scanningsignal is respectively located in the center of rotation D2.

The principle of angle measuring, known per se from WO 01/38828 A1, isrepresented in FIG. 2 by a one-dimensional grating 7.3. Reference isexpressly made to the disclosure of WO 01/38828 A1 regarding details ofthe principle.

The joints 2 and 4 are gimbal-mounted joints or magnetically prestressedball joints without play as described in DE 35 04 464 C1 mentioned atthe beginning.

Advantageously the support 3 constitutes a linear guide of the scanningunit 6.2 with respect to the scale 6. The support 3 furthermoreconstitutes a covering for the angle-measuring apparatus 7 and protectsit against extraneous light and the effects of the environment.

A further exemplary embodiment of a position measuring device 100 isrepresented in FIG. 3. Here, an interferometer 60 is employed as thelinear measuring device. It includes for example, of a laser 61, a beamsplitter 62 and, as a light source, a fiber-optical waveguide 63 with aball head 64. The ball head 64 is located in the center of rotation D4.The diverging light beam L reaches a beam splitter 65 for generating twolight portions L1 and L2. The one light portion L1 is used for the abovedescribed angle measurement in that the diverging light beam L1 ismodulated as a function of the grating 7.3 and the intensity pattern Mis detected by a detector 7.2. The other light portion L2 reaches aretro-reflector 66, is reflected there and again coupled into thefiber-optical waveguide 63. The evaluation of the reflected light beamL2 and the interferential determination of the linear displacement ofthe movable element 5 with respect to the base body 1 along the support3, not represented in FIG. 3, takes place in a manner known per Se.

The center of the retro-reflector 66 is located in the center ofrotation D2, and the detector 7.2 in the image D2′, generated by thebeam splitter 65, of the center of rotation D2. The reverse is alsopossible, so that then the detector 7.2 is located in the center ofrotation D2 and the center of the retro-reflector 66 in the image D2′.

The above-described position measuring devices 10, 100 areadvantageously employed for checking the positioning accuracy of aprogram-controlled machine element, in that the movable element 5 isfixed in place on the program-controlled machine element, for example adevice arm of a robot or a spindle of a machine tool, and the base body1 is fixed in place on a base element of the machine, i.e. the workpiecesupport of a machine tool. The spindle 5′ of a machine tool, as well asthe workpiece support 1′ are represented schematically by dashed linesin FIG. 1.

The employment of the above described position measuring devices 10 or100 for detecting a moved element in six degrees of freedom isrepresented in FIG. 4. Three telescope-like position measuring devices10 or 100 are hingedly arranged on one side on the base body 1, andhingedly on the element 5 on the other side for detecting the spatialposition of the element 5, as well as the orientation of theplate-shaped element 5 in regard to the base body 1.

If only five degrees of freedom are to be detected, two positionmeasuring devices 10 or 100 are sufficient.

A further use of the position measuring device 10 or 100 is representedby way of example in FIG. 5. The spatial position, as well as theorientation, of a spindle support 8 of a machine tool can be adjusted bymeans of several length-adjustable struts 9. The spindle support 8 canbe pivoted in all directions via a central column 11 and is hinged in alength-adjustable manner on the base body 1. The inclination of thecentral column 11, and therefore the orientation of the spindle support8 with respect to the center of rotation D2, as well as the lineardisplacement of the spindle support 8 in the direction of thelongitudinal axis of the central column 11, can be measured by aposition measuring device 10 or 100 in accordance with the presentinvention.

Further embodiment variations of the method in accordance with thepresent invention of course exist besides the explained example.

1. A position measuring device for detecting the spatial position of amovable element in relation to a base body, comprising: a linearmeasuring device that measures a distance between a movable element anda base body; a length-adjustable support connecting said movable elementwith said base body; a joint, by which said support is seated, pivotablein all directions around a center of rotation, in said base body,wherein said linear measuring device measures said linear displacementalong said support; an angle-measuring apparatus that measures apivoting angle between said support and said base body; a light sourcethat directs light along a beam path; a detector within said beam path;and a grating within said beam path between said light source and saiddetector, wherein for measuring said pivoting angle said beam pathextends between said movable element and said base body so that anintensity strip pattern is created by illuminating said grating by saidlight source, whose position relative to said detector is a measure ofsaid pivoting angle.
 2. The position measuring device in accordance withclaim 1, further comprising a second joint that is arranged between saidsupport and said movable element, by which said movable element isseated, pivotable around a second center of rotation, on said support.3. The position measuring device in accordance with claim 1, whereinsaid light source is arranged in said center of rotation.
 4. Theposition measuring device in accordance with claim 1, wherein a centerof light-sensitive elements of said detector is arranged in said centerof rotation.
 5. The position measuring device in accordance with claim2, wherein said light source is arranged in said center of rotation, anda center of light-sensitive elements of said detector is arranged insaid second center of rotation.
 6. The position measuring device inaccordance with claim 1, wherein said joint is a gimbal-mounted joint.7. The position measuring device in accordance with claim 2, whereinsaid joint is a gimbal-mounted joint and said second joint is agimbal-mounted joint.
 8. The position measuring device in accordancewith claim 1, wherein said joint is a magnetically prestressed balljoint.
 9. The position measuring device in accordance with claim 1,wherein said joint is a magnetically prestressed ball joint and saidsecond joint is a magnetically prestressed ball joint.
 10. The positionmeasuring device in accordance with claim 1, further comprising: ascanning unit of said linear measuring device; and wherein said supportcomprises: a first telescoping element comprising a scale attachedthereto; a second telescoping element telescopically attached to saidfirst telescoping element, wherein said scanning unit is fastened onsaid second telescoping element and said scanning unit scans said scale;and a cover for said angle-measuring apparatus.
 11. The positionmeasuring device in accordance with claim 1, wherein said linearmeasuring device is an interferometer.
 12. The position measuring devicein accordance with claim 11, wherein said light is split into a firstpartial beam for said angle-measuring apparatus and a second partialbeam for said linear measuring device.
 13. The position measuring devicein accordance with claim 1, wherein said grating is a two-dimensionalcross grating that generates a two-dimensional intensity pattern, whoseposition in relation to said detector is a measure of said angle.
 14. Aposition measuring system comprising: a program-controlled machinecomprising: a base element; and a movable portion that moves relative tosaid base; a position measuring device comprising: a linear measuringdevice that measures a distance between a movable element that is fixedto said base element and a base body that is fixed to said base element;a length-adjustable support connecting said movable element with saidbase body; a joint, by which said support is seated, pivotable in alldirections around a center of rotation, in said base body, wherein saidlinear measuring device measures said linear displacement along saidsupport. an angle-measuring apparatus that measures a pivoting anglebetween said movable element and said support; a light source thatdirects light along a beam path; a detector within said beam path; and agrating within said beam path between said light source and saiddetector, wherein for measuring said pivoting angle said beam pathextends between said movable element and said base body so that anintensity strip pattern is created by illuminating said grating by saidlight source, whose position relative to said detector is a measure ofsaid pivoting angle.
 15. The position measuring system in accordancewith claim 14, further comprising a second joint that is arrangedbetween said support and said movable element, by which said movableelement is seated, pivotable around a second center of rotation, on saidsupport.
 16. The position measuring system in accordance with claim 14,further comprising: a scanning unit of said linear measuring device; andwherein said support comprises: a first telescoping element comprising ascale attached thereto; a second telescoping element telescopicallyattached to said first telescoping element, wherein said scanning unitis fastened on said second telescoping element and said scanning unitscans said scale; and a cover for said angle-measuring apparatus. 17.The position measuring system in accordance with claim 14, wherein saidlinear measuring device is an interferometer.
 18. The position measuringsystem in accordance with claim 17, wherein said light is split into afirst partial beam for said angle-measuring apparatus and a secondpartial beam for said linear measuring device.